Enhancing The Perforamnce Of Mo-based Nano-/Micro-catalysts For The Hydrogen Evolution Reaction

Electrochemical water splitting has been considered as one the most reliable methods to produce hydrogen energy.Prior to the application,development of high-performance cataltysts is essential to reduce the overpotentials for both the hydrogen evolution reation（HER）and the oxygen evolution reaction（OER）.Recently,MMoO₄（M=transition metal ions）nano-/micro-structures has attracted considerable attion in the development of effecitent electrocatalysts for a set of reasons:（i）Large-scale synthesis of MMoO4microrod arrays can be achieved via hydrothermal reactions on the surface of Ni foam;（ii）the catalytic performance of MMoO₄ nano-/micro-materials can be promoted via the use of different combination of M;and（iii）MMoO4 nano-/micro-materials can be transformed into other high-performance ally nanoparticle catalysts.Owing to the above-mentioned reasons,the objective of this thesis is to explore new methods to enhance the catalytic performance of MMoO4 nano-/micro-structures in HER.It contains two research works:1.Enhancing electrochemical hydrogen evolution performance of CoMoO4-based microrod arrays in neutral media through alkaline activation.The results show that activation of CoMoO₄-based microrod arrays in KOH（1.0 M,2 h）allows one to significantly improve their electrochemical hydrogen evolution performance in phosphate buffer solution（1.0 M,pH=7.1）.The results the need for a low overpotential of 30 m V（vs.RHE）to deliver a current density of 10 mA cm^-22 in the neutral media,This value is even lower than the required overpotential for Pt/C（49 mV）.Mechanistic studies suggest that the improved performance is a result of the growth of Co（OH）2 nanosheets on the surface of the CoMoO4-based microrod arrays in the activation step,which has shown the ability to improve water molecule disassociation in the catalysis.In addition,the Co（OH）2nanosheets have the function of stabilization of the catalytic activity of the two-component catalysts by decreasing their overpotentials to deliver a designed current density.When combined with the intrinsic highly catalytic activity of P-doped CoMoO4,the strategy allows the preparation of a new class of superior electrochemical hydrogen evolution catalysts of Co（OH）2-P-doped CoMoO4 microrod arrays suitable for working in neutral media.By making use of the new catalysts and NiFe double hydroxide as cathodic and anodic electrodes,respectively,a two-electrode electrolysis device was created for neutral overall water splitting.Our results showed a low cell voltage of 1.78 V that needs for delivering a current density of 10 mA cm^-22 in the neutral electrolyte,even outperforming the state-of-the-art catalyst combination of Pt/C‖RuO₂ in terms of catalytic activity and stability.These findings suggest that alkaline activation may be utilized as a facile but useful strategy towards the creation of two-component catalysts for efficient hydrogen evolution in both basic and neutral media.2.Hierarchical Mo–Ni alloy nanoparticles as a bifunctional catalyst for ultrastable and efficient H2 production via membrane-free hybrid water electrolysis.In this work,hierarchical Mo–Ni alloy nanocatalysts was produced by reduction of NiMoO₄ microrod arrays in H₂ atmosphere at 500 ^oC for 2 h.The hierarchical bifunctional catalyst couple was used to accelerate the kinetics and stability of H2 production via the integration of the electrochemical reforming of benzyl alcohol（BA）and the HER in 1.0 M KOH.The high-performance of the hierarchical Mo–Ni nanoparticle catalyst for both the HER and the BA oxidation not only eliminated the need for an ion-conducting membrane to separate the cathodic and anodic reactions to achieve nearly unity faradaic efficiences for the two reactions,but also allowed the reactions to be readily driven by low cell voltage in a two-electrode configuration.The membrane-free hybrid water electrolysis technology exhibits a set of advantages including long device lifetime,ease of H₂ collection,and high efficiency,thus showing significant promise for practical H₂ production,especially considering the fact that the device can be readily powered by a solar cell under natural sunlight irradiation.